1. Field of the Invention
The invention relates generally to oil and gas production. Particularly, the invention relates to apparatus and methods for use in downhole operations.
2. Background of the Invention
Hydrocarbon fluids such as oil and natural gas are obtained from subterranean geologic formations by drilling a well that penetrates the hydrocarbon-bearing formations. Once a wellbore is drilled, the well must be completed before hydrocarbons can be produced from the well. Well completion may involve the design, selection, and installation of various equipment and materials in or around the wellbore for reinforcing the wellbore, conveying, pumping, or controlling the production or injection of fluids. After the well has been completed, production of oil and gas can begin.
One major objective in well completion is sand control. During production, sand or silt may flow into the wellbore from unconsolidated formations. This can lead to an accumulation of fill within the wellbore, reduced production rates and damage to subsurface production equipment. Migrating sand has the possibility of packing off around the subsurface production equipment, or may enter the production tubing and become carried into the production equipment. Due to its highly abrasive nature, sand contained within production streams can result in the erosion of tubing, flowlines, valves and processing equipment. The loss of material from the reservoir matrix can also lead to the movement and possible collapse of the reservoir. The problems caused by sand production and the deterioration of the reservoir support matrix can significantly increase operational and maintenance expenses and can lead to a total loss of the well.
One means of controlling sand production is the placement of relatively large grain sand or resin beads, referred to as gravel. The gravel serves to consolidate and prevent the movement of failed sandstone and/or increase the compressive strength of the formation sand. It can also serve as a filter to help assure that formation fines and formation sand do not migrate with the produced fluids into the wellbore. In a typical gravel pack completion, gravel is mixed with a carrier fluid and is pumped in a slurry mixture through a conduit, often drill pipe or coiled tubing, into the wellbore. The carrier fluid in the slurry is returned to the surface through a separate tubular or an annulus area, leaving the gravel deposited in the formation, perforation tunnels and wellbore where it forms a gravel pack. The carrier fluids may also leak into the formations, increasing the time and costs of performing gravel packing. Therefore, fluid loss control is often an integral part of gravel pack operations.
In addition to completion, specialized fluid loss control agents are used to control fluid loss during drilling, workover and stimulation operations. These fluid loss control agents are typically designed to control fluid losses for the duration needed in the applications. However, depending on the agents used in the fluid loss control compositions, these agents themselves may be damaging to the formations if allowed to remain in the formations. Therefore, when the fluid loss control is no longer needed, these fluid loss control agents may need to be removed so that they do not damage the formations. Removal of the fluid loss control agents typically involves pumping or adding a “breaker” to make the fluid loss control agents less viscous or more soluble.
In fluid loss control and many other downhole operations, controlled addition of chemicals and/or fluids is often required. These chemicals or fluids are typically pumped from the surface via tubings or conduits that extend to the desired zones in the wellbore. When pumped from the surface, a large volume will need to be pumped before the chemicals or reagents reach the desired zones. In addition, it is more difficult to time and quantify the chemicals or reagents that are needed. Therefore, there remains a need for better apparatus and methods that allow better control of deployment of chemicals or reagents downhole.